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Updated: Apr 2, 2026
Procoagulant Platelet Characterization by Measuring Phosphatidylserine Exposure and Microvesicle Release from Human Purified Platelets
Published on: November 29, 2024
TMEM16F is required for phosphatidylserine exposure and microparticle release in activated mouse platelets
Toshihiro Fujii1, Asuka Sakata2, Satoshi Nishimura3
1Laboratory of Biochemistry & Immunology, Immunology Frontier Research Center, Osaka University, Osaka 565-0871, Japan; Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Saitama 332-0012, Japan;
Abstract:
Phosphatidylserine (PtdSer) exposure on the surface of activated platelets requires the action of a phospholipid scramblase(s), and serves as a scaffold for the assembly of the tenase and prothrombinase complexes involved in blood coagulation. Here, we found that the activation of mouse platelets with thrombin/collagen or Ca(2+) ionophore at 20 °C induces PtdSer exposure without compromising plasma membrane integrity. Among five transmembrane protein 16 (TMEM16) members that support Ca(2+)-dependent phospholipid scrambling, TMEM16F was the only one that showed high expression in mouse platelets. Platelets from platelet-specific TMEM16F-deficient mice exhibited defects in activation-induced PtdSer exposure and microparticle shedding, although α-granule and dense granule release remained intact. The rate of tissue factor-induced thrombin generation by TMEM16F-deficient platelets was severely reduced, whereas thrombin-induced clot retraction was unaffected. The imaging of laser-induced thrombus formation in whole animals showed that PtdSer exposure on aggregated platelets was TMEM16F-dependent in vivo. The phenotypes of the platelet-specific TMEM16F-null mice resemble those of patients with Scott syndrome, a mild bleeding disorder, indicating that these mice may provide a useful model for human Scott syndrome.
Insights
Transmembrane protein 16F (TMEM16F) is crucial for phosphatidylserine (PtdSer) exposure on activated platelets, essential for blood coagulation. TMEM16F-deficient mice exhibit bleeding defects, modeling human Scott syndrome.
Area of Science:
- Hematology
- Molecular Biology
- Biochemistry
Background:
- Phosphatidylserine (PtdSer) exposure on activated platelets is vital for blood coagulation, serving as a platform for clotting factor complex assembly.
- This process is mediated by phospholipid scramblases, but the specific enzyme in platelets remained largely unidentified.
Purpose of the Study:
- To identify the specific phospholipid scramblase responsible for PtdSer exposure in mouse platelets.
- To investigate the role of this scramblase in platelet function and hemostasis.
- To establish a mouse model for Scott syndrome.
Main Methods:
- Platelet activation assays using thrombin/collagen or Ca(2+) ionophore.
- Analysis of PtdSer exposure and microparticle shedding in wild-type and TMEM16F-deficient platelets.
- Assessment of thrombin generation and clot retraction.
- In vivo thrombus formation imaging.
- Genetic manipulation to create platelet-specific TMEM16F-deficient mice.
Main Results:
- TMEM16F was highly expressed in mouse platelets and mediated Ca(2+)-dependent PtdSer exposure.
- TMEM16F deficiency impaired PtdSer exposure and microparticle shedding but not granule release.
- Thrombin generation was significantly reduced in TMEM16F-deficient platelets.
- In vivo thrombus formation demonstrated TMEM16F-dependent PtdSer exposure.
Conclusions:
- TMEM16F is the primary phospholipid scramblase mediating PtdSer exposure in activated platelets.
- TMEM16F plays a critical role in hemostasis by facilitating thrombin generation.
- Platelet-specific TMEM16F-null mice serve as a valuable model for studying Scott syndrome.
